<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="https://s3.pstatp.com/cdn/expire-1-M/jquery/3.1.1/jquery.min.js"></script>
    <title>Document</title>
    <style>
        body {
            margin: 0px;
            padding: 0px;
        }

        .content {
            margin: 0 auto;
            background-color: skyblue;
            width: 500px;
            height: 500px;
            line-height: 500px;
        }
    </style>
</head>

<body>
    <div class="content">
        <input type="file" id="f1" onchange="getFile()">
    </div>
    <div id="test">
        123
    </div>
    <script>
        function getFile() {
            const file = document.getElementById('f1').files[0];
            console.log('file', this, file);
        }
        function test() {
            console.log('test', this);
        };
        test.prototype = new test();

        $(() => {
            $('#test').css('color','#f00')
        });

    </script>
</body>

</html>